Vesicular stomatitis virus is a nonsegmented negative-stranded RNA virus. The virion consits of a central ribonucleoprotein core surrounded by a membrane, and contains five viral structural proteins: L ( a polymerase subunit) 2,109 aa; G (the surface glycoprotein) 511 aa; M (the matrix protein) 229 aa; NS ( a phosphorylated polymerase subunit) 225 aa: N (the nucleoprotein) 422 aa. The RNA genome (11,162 nucleotides) comprises six transcription units: five genes in the order 5'L,G,M,NS,N 3' and a 47 inculeotide 3'-proximal leader. In the infected cell the RNA genome, complexed with the N protein, serves as a template for two distinct but coupled pathways of RNA synthesis: transcriptin and replication. The products of transcription are the plus strand leader and five monocistronic mRNAs which possess the 5'-terminal cap structure 7mG(5') ppp(5')Am and a 3'terminal poly(A) track. The products of replication are genome-length positive- and negative-stranded RNAs which are encapsidated with N protein. Transicription of VSV mRNAs is mediated by a subviral complex which comprises a two subunit transcriptase (L and NS), the ribonucleoprotein template, and at least five enzymatic activitiess: polymerase, guanylyltransferase, guaine-7- methyltransferase, nucleoside-2' -0-methyltransferase, and protein kinase. The long range goal of this program is to define the stucture-function correlates within the complex. To this end, three experimental approaches are being integrated: 1) site- directed photoaffinity protein labeling to identify and localize enzyme active sites; 2) nucleotide sequence determination to provide the predicted amino acid sequecne of L, identification of conserved regions in L, and identification of sites of mutational lesions in the l. gene; 3) in vitro functional analyses of transcription variants. Correlation of the data generated in these studies will lead to a comprehensive model for VSV transcription. VSV serves as an excellent model system for the study of negative- strand RNA viruses, many of which are important pathogens of man. Information generated in the VSV studies studies described herein will lead to strategies for the prevention and treatment of negative trand viral diseases of man.